1. Field of the Invention
The present invention relates to a vacuum processing apparatus used for processing a board-like workpiece such as a semiconductor wafer or a liquid crystal display to perform processing such as fine patterning or the like by use of a plurality of gases.
2. Description of the Related Art
A vacuum processing apparatus is provided with a processing unit including a vacuum vessel internally having a process chamber called a process unit, an exhaust device, a plasma forming device and the like. Such a vacuum, processing apparatus requires low costs and improved productivity. In particular, the vacuum processing apparatus has a major problem in that throughput (the number of boards processed per unit hour) is improved to increase efficiency of processing per apparatus. In the following, a semiconductor processing apparatus is partially described as an example; however, the present invention is not limited to the semiconductor processing apparatus. The processing performed by the semiconductor processing apparatus, one of the vacuum processing apparatuses, includes a step of subjecting a workpiece such as a semiconductor wafer which is a board to be processed, to processing under vacuum, e.g., plasma processing such as etching or the like. In order to perform such processing with high throughput, i.e., to increase efficiency of processing per apparatus, a semiconductor processing apparatus provided with a plurality of process chambers is used. Semiconductor processing apparatuses are generally known that include a process chamber and an atmospheric transport chamber under ordinary pressure.
A cassette storing the predetermined number of, e.g. 25, wafers is mounted on the front side of the semiconductor processing apparatus as described above. A transfer robot takes the wafers one by one out of the cassette and transfers those to a load lock that is adopted to be switched between atmosphere and vacuum. Thereafter, the wafer is transferred from the load lock depressurized through vacuum evacuation via a depressurized transfer path into any one of process chambers in which the wafer is processed. After the processing, the wafer is transferred from such a process chamber, passing through the path in a direction reverse to that during the loading, via the load lock to under the atmospheric pressure. Thereafter, the wafer is returned to the same position in the same cassette from which it was transferred by the transfer robot. This is the general order of the actions in processing the wafer in the semiconductor processing apparatus.
In order to improve throughput in a series of actions in the semiconductor processing apparatus, it is conceivable to improve a transfer rate of a workpiece or to reduce processing time. In recent years, the processing time has been reduced; therefore, the semiconductor processing apparatus requires an improvement in transfer rate.
JP-A-2009-94530 (patent document 1) discloses a mechanism in which a transfer robot can concurrently transfer workpieces to a plurality of corresponding process chambers by extension and retraction of two arms thereof, and a method of achieving high-throughput by use of the mechanism. However, processing gases may be different in type from each other. In such a case, it is necessary to transfer the workpieces in such a manner as to prevent gases from mixing with each other, in order to prevent processing accuracy from being degraded and a workpiece from being contaminated.
To meet the necessity, patent document 1 discloses the method of preventing the gases from mixing with each other by increasing the pressure outside the process chamber to reduce an amount of contaminated matter containing the processing gases that is discharged outwardly from the process chamber.